The best and the worstI've skied many days at W/B over the last 20 years or so and have to agree with most of the comments. W/B has the best and most diverse terrain in all of North America. It has more in-bounds extreme terrain than any other resort, but its tremendous alpine area is also very accessible to intermediate skiers. On a good day, W/B cannot be beat.
That said, on a bad day W/B is the worst. Weather and timing will make or break your experience. W/B is often foggy, it is often rainy, the snow quality is often poor, and it can be crowded. While I've had some great days at W/B, I've had more mediocre days than I can count.
Everybody should go to W/B at least once, but you are foolish if you book a trip in advance there. W/B is very expensive and frankly, it isn't worth it a lot of the time. The same applies with buying multi-day passes when you are there. I didn't take my own advice this February and we only skied two of our five days because of the rain, poor visibility, and all-around lousy conditions.
If you have to book in advance, the other approach would be to book a longer trip. If you can book several weeks, you have a much better chance of hitting some good days. The amount of terrain on both mountains is too great to explore in a week anyway and there is a lot to do in the village.
January and March are typically the best snow months. You should use caution in Febrary--historically it is the month with the least snow and (in my experience is the most rain-prone of the winter months).